The invention relates to liquid dispensing systems and, in particular, to dispensing systems for dispensing a heating liquid.
Dispensing systems are used in numerous manufacturing production lines for dispensing heated liquids onto a substrate at specified application temperatures. Often, the dispensing system must discharge the heated liquid within a precise, elevated temperature range, such as in the dispensing of hot melt adhesives. Certain hot melt adhesive dispensing systems include a bank of individual dispensing modules or applicators that have a nozzle and an internal valve assembly for regulating liquid flow through the nozzle. Often, the valve assembly includes a valve seat engageable by a movable valve stem for flow control purposes.
The dispensing modules are typically heated to a desired adhesive application temperature such as by being directly connected to a heated manifold. In addition, a flow of heated process air is provided to the vicinity of the adhesive discharge outlet or nozzle. The heated process air is used for modifying a characteristic of the dispensed hot melt adhesive. For example, hot air streams can be angularly directed onto the extruded stream of hot melt adhesive to create one of various different patterns on the substrate, such as an irregular back-and-forth pattern, a spiral, a stitch pattern, or one of a myriad of other patterns. To form the pattern, the hot air stream imparts a motion to the discharged stream, which deposits continuously as a patterned bead on a substrate moving relative to the stream. As another example, the heated process air may be used to attenuate the diameter of the molten adhesive stream.
The heated process air also maintains the temperature of the nozzle at the required adhesive application temperature so that the hot melt adhesive will perform satisfactorily. If the nozzle is too cool, the hot melt adhesive may cool down too much just prior to discharge. The cooling may adversely affect the liquid cut-off at the nozzle when the valve stem is closed so that accumulated hot melt adhesive in the nozzle can drip or drool from the dispensing module. Often, this dispenses hot melt adhesive in unwanted locations such as, for example, in undesirable locations on the substrate or on the surrounding equipment and reduces edge control for the adhesive bead desired for intermittent dispensing applications. Furthermore, if hot melt adhesive exits the nozzle at a reduced temperature, the reduction in temperature can compromise the quality of the adhesive bond.
Conventional hot air manifolds employed in adhesive dispensing systems consist of a metal block having an interconnected network of internal air passageways and one or more heating elements. Process air is introduced into an inlet of the network and is distributed by the various air passageways to a set of outlets. Each outlet provides heated process air to an individual dispensing module. The heating elements heat the metal block by conductive heat transfer, and the surfaces of the internal air passageways, in turn, transfer heat energy to the process air circulating in the network. The heat energy heats the process air to a desired process temperature.
Conventional hot air manifolds are machined for a specific dispensing application. To place the outlets at desired locations, bores creating the air passageways must be machined as cross-drilled passages having precise inclination angles between two sides of the distribution manifold. The pattern of bores is challenging to design and complex to create. In addition, the pattern of outlets cannot be altered for accommodating differing numbers of dispensing modules or for adjusting the spacing between adjacent ones of the dispensing modules. In addition, because a single hot air manifold serves all of the modules, it is difficult if not impossible to individually adjust a property of the heated air, such as flow rate, provided to individual ones of the dispensing modules.
The introduction of modular adhesive manifolds for hot melt adhesive dispensing systems has provided a heretofore unsatisfied need for a modular hot air manifold. Conventional hot air manifolds that distribute heated process air to multiple outlets are not well suited for modular adhesive dispensing systems. In fact, conventional hot air manifolds actually reduce the key advantage of such systems since the hot air manifold cannot accommodate differing numbers of module adhesive manifolds (for changing the number of dispensing modules).
Thus, a hot air manifold is needed that has reduced dimensions and that can be dedicated to individual dispensing modules among those modules in a bank of dispensing modules. In particular, a hot air manifold is required for use with modular adhesive dispensing systems. A system is also needed for dispensing liquids with the assistance of process air.